The present invention relates to gelatin capsules, both hard shell and soft shell or softgels, consisting of an envelope or shell comprising gelatin and optionally a plasticizer and a capsule filling containing at least one active substance and/or a dietetic agent or foodstuff as well as a solvent mixture, and to a process for preparing such capsules or softgels.
Soft gelatin capsules or softgels are predominantly used to contain liquids wherein the active ingredients are present in the dissolved or suspended state. The employed filling materials commonly include vegetable oils, animal oils and mineral oils, liquid hydrocarbons, ethereal oils and polyethylene glycol. Fats and waxes are also commonly used or added to the fill for increasing the consistency.
In recent years, there have also been developed processes for filling liquids and pasty filling materials into two piece, telescoping hard gelatin capsules.
A particularly good bioavailability of pharmacologically active substances in the fill of the gelatin capsules is attained if the active substance is successfully dissolved in a suitable solvent and the encapsulated solution is administered to a patient. However, such solvents may only include adjuvants which, on the one hand, are acceptable for application to the human organism and, on the other hand, do not impair the stability of the gelatin shell or envelope.
As discussed in DE-OS 33 07 353, there are known soft gelatin capsules or softgels containing, as a solvent, polyethylene glycol having an average molecular weight of 600 as well as glycerol and/or 1,2-propylene glycol. These soft gelatin capsules have proven to be very valuable. However, such polyethylene glycols are considered to be unsuitable solvents for some active substances. There are sensitive action materials such as, for example, sulfonamides or organic iodine compounds which are chemically instable in polyethylene glycols. Furthermore, a number of active substances have been known, for example, phenols or phenobarbital, for which a complex formation occurs between the ethoxyl groups of the polyethylene glycols and the active substances, which complexes cause a reduced bioavailability of the active substances to result. Eventually, there are also higherdosed active materials, for example pentetrazole, which are not sufficiently soluble in polyethylene glycols.